Science

A nearby star has completely destroyed its planet’s atmosphere

A nearby star has completely destroyed its planet’s atmosphere

What if you put an Earth-sized planet in close orbit around an M-dwarf star? This is more than an academic question because M dwarfs are the most numerous stars we know. A group of astronomers studying the planet GJ 1252b has found the answer, and it’s not pretty.

Because this planet is so close to its star, it receives a lot of heat. And that proximity is deadly in another way. “The star’s radiation pressure is enormous, enough to blow up the planet’s atmosphere,” said Michelle Hill, an astrophysicist at the University of California Riverside and co-author of a recent paper focusing on GJ 1252b. The planet is located about 65 light years from Earth and orbits its star twice every 24 Earth hours. The heat of the star makes this world inhospitable.

An illustration of the atmosphere swept away from a planet by a nearby star. (NASA)

This is not very different from Mercury in our solar system. It has no atmosphere and the planet alternately warms and freezes as it orbits the Sun. In fact, the Earth also loses some atmosphere due to solar activity. However, volcanism and other processes release the gases back into our atmosphere. Earth is lucky; planets like Mercury and GJ 1252b are not. And, it has profound implications for the search for life on friendly worlds.

What is it about M dwarf stars?

There are millions and millions of M dwarf stars in our galaxy alone. Their size ranges from about one-tenth to two-thirds of the mass of the Sun. They can be active, sending flares and fallouts through their systems. Most of them have at least one planet in their habitable zones and others at different distances.

Not a great combination if you want to find life on their planets. Stellar activity that blasts planetary atmospheres apparently also destroys any chance of life on those worlds. And because M dwarfs are so numerous, their ubiquity can reduce the number of planets in the galaxy that actually support life. That’s not great news for planets like GJ 1252b.

“It’s possible that the condition of this planet bodes poorly for planets even further away from this type of star,” Hill said. “That’s something we’ll learn from the James Webb Space Telescope, which will be looking at planets like these.”

While M dwarfs might be atmosphere killers, it’s not all doom and gloom. For example, many of the 5,000 stars in Earth’s solar neighborhood are M dwarfs. Even if a large fraction of them make their planets hospitable, at least 1000 others (not all of them M dwarfs) could create conditions suitable for life on their worlds. “If a planet is far enough away from an M dwarf, it could potentially retain an atmosphere. “We can’t yet conclude that all the rocky planets around these stars are down to Mercury’s fate,” Hill said. “I remain optimistic.”

Search for the atmosphere of GJ 1252b

The science behind the situation on GJ 1252b is intriguing. Astronomers used data from the Spitzer Space Telescope to estimate the planet’s infrared radiation as the secondary eclipse blocked its light. Measurements showed that the star was blowing up the planet. Daily surface temperatures hover around 1227 C (2242 F). It is hot enough to melt gold, silver and copper.

The heat, along with the presumed low surface pressure, led researchers to believe there was no atmosphere there. But let’s assume for a moment that there was an atmosphere of carbon dioxide. This would keep the heat on the surface and perhaps allow that cover to last for a while. However, it turns out that GJ 1252b is not so lucky. “A planet could have 700 times more carbon than Earth and still not have an atmosphere. It would build up at first, but then shrink and erode,” said Stephen Kane, a UCR astrophysicist and co-author of the study.

In the long run, if this study holds for a significant population of M dwarf stars, it will shift the search for habitable planets to other candidates around less unstable stars.

For more information

The discovery could dramatically narrow the search for space creatures
GJ 1252b: A hot terrestrial super-Earth with no atmosphere
M Dwarf stars



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